L5-S1 disc replacement after two previous fusion surgeries for scoliosis

Following scoliosis surgery, lumbar motion segment degeneration below the level of fusion is not uncommon. Especially long fusions extending to the mid and lower lumbar spine increase the likelihood of degeneration of the remaining motion segments. The management for these patients is controversial and depends on the clinical presentation and level of degeneration. The increasing confidence in motion-preserving technology leads to a dilemma on whether to fuse the remaining lumbar levels or risk utilising disc arthroplasty to preserve the remaining motion segments and facilitate coronal balance in patients with previous long fusion for scoliosis. We present an interesting case of a 44-year-old lady, who underwent two-stage corrective surgery for progressive idiopathic scoliosis at the age of 22 years. In the first stage, she had T11-L3 anterior fusion, whilst in the second stage posterior fusion was done from T5 to L3. At 22 years after the initial surgery, she presented with worsening low back pain and bilateral L4 radicular symptoms. MRI scan confirmed severe disc degeneration at L3-4 and L5-S1 levels with preserved L4-5 disc. She initially underwent L3-L4 decompression and posterolateral fusion at that level, which relieved her radicular symptoms. However, she had persistent pain at the lumbosacral junction with Modic I changes. The options of an anterior L5-S1 fusion or disc replacement were considered and discussed with the patient. The disc replacement option was decided upon with the patient, as anterior fusion was judged to increase the risk of coronal imbalance. At the 1-year follow-up, she reported significant improvement in the back pain. The radiographs at 1 year showed satisfactory position and function of the artificial disc replacement. The disc was flexed laterally, accommodating the coronal balance of the spine. We conclude that L5-S1 motion segment can be preserved with artificial disc replacement in patients with previous long fusion for scoliosis surgery. The real difficulty arises when choosing between disc replacement and extension of fusion. In our patient, the disc replacement has worked well so far. However, the disc is clearly at a mechanical disadvantage, and loss of function in the mid- or long term would not be surprising.